Metallization interconnects are critical to the proper electronic function of semiconductor devices. Several advances in semiconductor processing have been aimed at improving signal transport speed by reducing metal interconnect resistivities and improving resistance to electromigration effects. Copper has increasingly become a metal of choice in, for example, upper levels of metallization in a multi-level semiconductor device due to its low resistivity and higher resistance to electromigration. Tungsten is still preferred for use in the lower metallization layers adjacent to the silicon substrate since it provides an effective diffusion barrier to metal diffusion from overlying metallization layers to react with the silicon substrate. Tungsten further has high resistance to electromigration and can effectively be used to fill high aspect ratio vias by chemical vapor deposition (CVD) processes.
A serious problem in tungsten plug formation according to prior art methods of using a dry etchback process to remove the tungsten metal above the via level is that during the dry etchback process residual metal containing particles ranging in size from about 0.5 microns to about 40 microns frequently remain on the wafer process surface. Following the tungsten etchback process a CMP process may be subsequently used to complete the removal of excess tungsten above the plug level or to remove an underlying barrier layer blanket deposited to line the plug prior to tungsten deposition. A major problem in tungsten plug formation process is the scratching of the process wafer surface caused by the residual particles or etching residue in a subsequent CMP process.
Prior art processes been attempted cleaning the wafer surface of tungsten particles by wet methods typically including deionized water together with scrubbing. These methods have not been entirely successful and have been found in many cases to fail to reduce the level of scratching in subsequent CMP processes.
Therefore, there is a need in the semiconductor processing art to develop a method for a reliable cleaning process following a metal etchback to remove metal containing etching residue produced during the metal etchback process in order to improve a subsequent CMP process.
It is therefore an object of the invention to provide a method for a reliable cleaning process following a metal etchback to remove metal containing etching residue produced during the metal etchback process in order to improve a subsequent CMP process while overcoming other shortcomings of the prior art.